Cyclic performance of exterior R.C beam-column strengthened with different thicknesses of CFRP sheets

The recent ground motion results indicated that the RC buildings are required to be retrofitted by different strengthening techniques. Nowadays, the external strengthening gain interest since its easy, cost effective and not required redesign of buildings. The CFRP sheets are suitable solution and utilized by a number of researchers. However, the numerical cyclic performance of connection strengthened with different thicknesses of CFRP need to be well investigated. This study assessed the performance of RC exterior beam column connection strengthened with CFRP sheets First, two grades of concrete are utilized to be control specimens, normal concrete compressive strength (C20) and high concrete compressive strength (C50) then, the specimens are retrofitted with different thicknesses (1.2, 2.4, 3.6mm) of CFRP sheets. The stresses and damage states showed the importance of connection retrofitting. The CFRP shift the plastic hinge zone away from the panel zone. Furthermore, the results demonstrated that by increase of CFRP thickness the connection resistance will be improved. The comparison between the hysteresis curves demonstrated that the yield and ultimate loading were enhanced for strengthened connection for both concrete grades and the incremental in thicknesses also increase them. The outputs also exhibited that the stiffness and ductility has increased for retrofitted specimens indicating that the CFRP comprehensively overcome the applied cyclic loading and the beam column connection is able to resist such type of loading.

Finite Element Analysis of Cracked One-Way Bubbled Slabs Strengthened By External Prestressed Strands

Bubbled slabs can be exposed to damage or deterioration during its life. Therefore, the solution for strengthening must be provided. For the simulation of this case, the analysis of finite elements was carried out using ABAQUS 2017 software on six simply supported specimens, during which five are voided with 88 bubbles, and the other is solid. The slab specimens with symmetric boundary conditions were of dimensions 3200/570/150 mm. The solid slab and one bubbled slab are deemed references. Each of the other slabs was exposed to; (1) service charge, then unloaded (2) external prestressing and (3) loading to collapse under two line load. The external strengthening was applied using prestressed wire with four approaches, which are L1-E, L2-E, L1-E2, and L2-E2, where the lengths and eccentricities of prestressed wire are (L1=1800, L2=2400, E1=120 and E2=150 mm). The results showed that each reinforcement approach restores the initial capacity of the bubbled slab and improves it in the ultimate load capacity aspect. The minimum and maximum ultimate strength of strengthened cracked bubbled slab increased by (17.3%-64.5%) and (25.7%-76.3%) than solid and bubbled slab, respectively. It is easier to improve behavior with an increased eccentricity of the prestressed wire than to increase its length.

Finite Element Analysis of Cracked One-Way Bubbled Slabs Strengthened By External Prestressed Strands

Bubbled slabs can be exposed to damage or deterioration during its life. Therefore, the solution for strengthening must be provided. For the simulation of this case, the analysis of finite elements was carried out using ABAQUS 2017 software on six simply supported specimens, during which five are voided with 88 bubbles, and the other is solid. The slab specimens with symmetric boundary conditions were of dimensions 3200/570/150 mm. The solid slab and one bubbled slab are deemed references. Each of the other slabs was exposed to; (1) service charge, then unloaded (2) external prestressing and (3) loading to collapse under two line load. The external strengthening was applied using prestressed wire with four approaches, which are L1-E, L2-E, L1-E2, and L2-E2, where the lengths and eccentricities of prestressed wire are (L1=1800, L2=2400, E1=120 and E2=150 mm). The results showed that each reinforcement approach restores the initial capacity of the bubbled slab and improves it in the ultimate load capacity aspect. The minimum and maximum ultimate strength of strengthened cracked bubbled slab increased by (17.3%-64.5%) and (25.7%-76.3%) than solid and bubbled slab, respectively. It is easier to improve behavior with an increased eccentricity of the prestressed wire than to increase its length.

Strengthening and Characterization of Existing Reinforced Concrete Beams for Flexure by Effective Utilization of External Steel Elements

Strengthening of structural members is a common practice around the world that may arise due to deterioration of concrete with age or upgradation of design code. This paper aims to elucidate a technique used for strengthening of the reinforced concrete beam for flexural capacity by using externally welded steel angles and steel bars. For this motive, three beams were strengthened with external steel angles and three with external steel bars. The external strengthening steel elements were attached at the bottom of the beam with shear reinforcement. Control samples without external steel angles and steel bars for comparison purposes were also prepared. All reinforced concrete beams were first constructed using a concrete ratio of 1:2:4, and then external steel elements were added to existing flexural reinforcement by using a fillet weld with tee joints having thickness and length of 5/16" (7.9 mm) and 6" (152.4 mm), respectively. Fourth point loading criteria were used to investigate the flexural capacity of beams in positive bending. All beams were designed strong enough in shear, to resist the ultimate loads without shear failure. Test results indicated that beams strengthened with this technique have an average increase of 238% with steel angles and 106% with steel bars, in load-carrying capacity than control samples. Strengthened beams showed a uniform crack pattern. Moreover, the concrete cover made a good bond with existing concrete and was strong enough to withstand ultimate loads. Conclusively, the steel angles and steel bars can be used as an external strengthening material, to enhance the flexural capacity of reinforced concrete beams.